COMBAT tv series helmets, notice the rough recorking on these Hollywood props, possibly not even made of steel, probably lightweight plastic, the shells dont even have chin strap loops / bales
I think you're correct with the photos you posted, BOLO. I've read by the second season of COMBAT they were using helmets (Hats) made of some type of plastic or styrofoam because the actors complained that real helmets weighed too much. Those are good stills showing the strange texture, and a good observation they don't even have chinstraps or bales.
Realism in WWII movies and TV mini-series are not perfect, but they've sure come a long way from the 60's. Even as a kid, it used to drive me crazy that the Germans used American M3 halftracks, and 'Dietrich' was their only nemesis in the entire desert week after week. Still, I never missed an episode.